Process and device for treating particulate material with electron beams

ABSTRACT

Process and device for electron beam treatment of bulk material where the bulk material is fed into a continuous stream by means of compression stages (3) which can be evacuated. It is dispersed and directed into a dosed irradiation chamber (1), passing in this chamber through an irradiation field in a free-fall process, and discharged from the irradiation chamber through a compression stage system (4). The invention enables electron beam treatment of biological materials to be carried out to particularly good advantage, e.g. in combatting harmful organisms in seeds.

DESCRIPTION

The present invention relates to a process for treating bulk material inparticulate form, in particular seeds, with electron beams within anirradiation field of an irradiation chamber through which the bulkmaterial is moved and subjected to an electron beam treatment with aplurality of electron beams and from which it is subsequentlydischarged, and to a device for such a treatment. The invention relates,in particular, to a process for treating grainy, moist or dustyparticulate material or bulk material with electron beams in vacuum.Preferably, the process and the device serve to treat seeds, inparticular grains, which are subjected to dressing with electron beamsto render the pathogens ineffective that adhere to these seeds.

BACKGROUND OF THE INVENTION

It is known that seeds are irradiated on all sides with low energyelectrons. Electron energy and radiation dose are chosen such that thesurface and near-surface layer are acted upon without any substantialimpairment of the embryo (DD-PS 242 337). A device is here known whichconstantly redistributes the seeds with the aid of moving means within arecipient, with the seeds being acted upon by a deflected and fannedelectron beam. Transporting devices which serve to supply and dischargethe seeds and include the associated feeders are connected to therecipient (U.S. Pat. No. 4,633,611).

Since especially with seeds a relatively great amount of water is boundto and in the surface of seeds, the water evaporation rate is very highat the vacuum required in the irradiation chamber. This fact can only becounteracted by taking great evacuation efforts. Moreover, the processas well as the device have the disadvantage that an industrialapplication which calls for a great throughput is not possible becauseof the great dust portion of the seeds. The long-term operation of theelectron gun is affected by this great dust development in theirradiation chamber.

Irradiation devices in the case of which the bulk material is guided ina free atmosphere are also known (U.S. Pat. No. 860,513 and 2,333,842).These devices are not suited for effecting any action on the surface orthe near-surface layer of the bulk material exactly in the prescribeddepth; in particular, phytotoxic effects on the seeds may occur becauseof the resultant energy dispersion.

FR-PS 961 079 discloses an irradiation device which has electron beamgenerators arranged opposite to each other on an irradiation chamber andin the case of which the material to be irradiated is introduced fromabove into the irradiation chamber and discharged therefrom downwards.Such a device, however, does not create the preconditions for anadequately individual irradiation of grainy bulk material, such asseeds, for dressing said material.

It was discovered during the conduction of the process with the knowntechnological electron beam devices and the known bulk material deliverydevices that relatively constant surface doses can only be achieved at asmall bulk material throughput. By contrast, all attempts have failed toachieve a uniform surface dose as is required by the process, as well asa high utilization degree of the electron beam and a high massthroughput with the device at the same time. In other words, evacuationproblems which can no longer be solved technically arise from otherdelivery principles that have accomplished this uniformity. However, thesolution of both problems is an absolutely necessary precondition for anindustrial utilization of the process.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to improve a processof the above-mentioned type in such a way that the bulk material inparticulate form is irradiated with electrons such that a highthroughput is possible at small dwell times within the recipient. Theprocess is above all suited for bulk material in particulate form, suchas seeds, with a relatively high water and/or dust content.

It is also the object of the present invention to provide a device fortreating bulk material in particulate form, in particular grain, withelectron beams, namely a device for irradiating the particulate materialby electron beams on all sides and as uniformly as possible, with theapparatus needed being as small as possible, and also for treatingmaterials which have a relatively high water and/or dust content.

As far as the process is concerned, the above-mentioned object isattained according to the invention in that the bulk material is movedin a free-fall process through the evacuated irradiation chamber indosed amounts and separated at an inlet side of the evacuated chamberfor forming a continuous material flow of separated particulatematerial, the electron beams are spread in the direction of fall of thematerial and the separated particulate material is irradiated in theirradiation field on substantially all sides by the spread electronbeams from several sides and different directions.

Hence, a material flow is formed from the particulate material and saidflow is moved through the evacuated irradiation chamber in which saidmaterial flow is guided in a free-fall process through at least oneirradiation field of the irradiation chamber, with the distance betweenthe particles being increased within the material flow, subjected to anelectron beam treatment in the irradiation field and subsequently guidedout of the irradiation chamber.

Preferably, the particulate material is supplied via at least onepressure stage to the irradiation chamber and discharged via at leastone further pressure stage out of the irradiation chamber.

It is here preferred that the particulate material or bulk material iscontrolled prior to its introduction and after its discharge from theirradiation chamber, preferably in front of and after a respectivepressure stage for introducing and discharging bulk material, optionallyalso in the irradiation chamber itself, in such a way that a column ofparticulate material or bulk material is formed which has a great heightor axial extension in comparison with its diameter and acts as a flowresistance.

To keep the critical release of degasification products or moistureand/or dust from the particulate material or bulk material as small aspossible with respect to the evacuation degree in the recipient and withrespect to a long, trouble-free operation of the electron beamgenerators used for electron treatment, it is preferred that theparticulate material or bulk material is transported during the stepwisepressure transition from atmospheric pressure to internal pressure in anevacuated irradiation chamber (recipient) in such a way that the amountof gases (water vapour) and dust sucked off by evacuation at eachpressure stage is as small as possible. Therefore, the internal pressureis preferably adjusted at the pressure stages such that the vapourpressure of water is not fallen below.

To achieve a uniform irradiation of the particles of the material flowor bulk material flow, it is ensured that the particles pass through theirradiation field at least at about the same particle speed.

To achieve a dosage distribution which is as uniform as possible on thesurface of the irradiated particle material, e.g. of seeds, the materialis exposed in the irradiation field of the irradiation chamber toelectron beams which are fanned over a very large width, and is actedupon along a path which begins above the exit point of the electron beamfrom an electron beam generator and ends below the same. This means thateach particle, e.g. seed, is preferably subjected during its free fallin the irradiation chamber within the irradiation field to an electronirradiation which is directed from obliquely upwards to obliquelydownwards relative to the electron beam generator. As a result, eachparticle is acted upon during its free fall for a relatively long timeand at least approximately from all sides.

It is preferred that the current density profile of the irradiationfield is configured in vertical direction, i.e. in the direction of fallof the particulate material or the bulk material flow in such a way thatthe surface dose of the material, e.g. of seeds, is substantially evenlydistributed. A current density profile may here be used for eachelectron beam generator which has two regions of a high current densitythat are acted upon over the entire width of the material flow in asufficiently uniform way and are generated by a region of small currentdensity or entirely absent actuation, with the current density profileof the electron beams used being optimized such that the particlespassing through this irradiation field, e.g. seeds, receive asufficiently homogeneous dosage distribution over their surface.

As another measure for homogenizing the surface dose on the irradiatedparticulate material, an evacuation or working pressure is adjusted inthe irradiation chamber to lie between about 10 Pa and some 100 Pa,preferably from about 100 Pa to several 100 Pa, whereby an angularscatter of the accelerated electrons is achieved without anyobjectionable energy losses.

The line frequency of the electron beam is preferably at several kHz andthe picture frequency within the range of some 10 kHz to some 100 kHZ.Electron beam power losses due to a long optical path up to the plane ofthe material flow of the particulate material or bulk material flow,blanking as well as other influences can be compensated by thisprogrammability of the deflection function in an advantageous way.

An especially preferred embodiment of the process for treating bulkmaterial with electron beams, in particular for treating seeds againstharmful organisms, is characterized in that the bulk material isintroduced into and discharged from an evacuated irradiation chamber viapressure stages, with a minimum pressure that corresponds at least tothe vapour pressure of a liquid, in particular water, in the nearsurface layers and on the surface of the bulk material prevailing ateach pressure stage for the introduction of the bulk material, and thesucking off of gases, in particular water vapour, and dust beingminimized, and that, after having passed through the pressure stages,the bulk material moves through the irradiation chamber in a free-fallprocess at approximately the same individual speed of the particles ofthe bulk material, the particles being separated at a transparency inthe irradiation region of about 50% and at a mean particle distance in adirection transverse to the flow direction of the bulk material which isgreater than the particle size, and is acted upon by a plurality offanned electron beams on several sides from obliquely upwards toobliquely downwards relative to the electron beam generation, with theelectron beam generation being carried out with two electron guns in aradially opposite arrangement relative to the bulk material flow.

In accordance with another embodiment of the present invention thecombination of the following steps has turned out to be of specialadvantage to an electron beam treatment of the particulate material orbulk material, in particular for combating harmful organisms on grains.The bulk material is transported in the irradiation chamber duringstepwise pressure transition from atmospheric pressure to evacuationpressure or working pressure in such a way that as little gases (watervapour) and dust as possible are sucked off by evacuation at eachpressure stage. The pressure at the pressure stages is adjusted suchthat the vapour pressure of water is not fallen below. The pressure inthe irradiation chamber is preferably kept within a range between 100 Paand some 100 Pa. After having passed through the pressure stages, thebulk material moves in a free fall at approximately the same individualspeed of the particles of the bulk material flow, e.g. seeds or grains,through the irradiation chamber and is acted upon by a plurality offanned electron beams. The particles are separated in the material orbulk material flow in such a way that the transparency in theirradiation range is about 50% and the mean distance between theparticles in a cross-sectional plane of the irradiation chamber isgreater than their size (outer dimension). In this region the electronbeams from electron guns act on the particles at least on two sides andpreferably at about the same time. The electron beams are fanned over avery great width and therefore act on the particles on several sidesalong the flow path of said particles, i.e. from obliquely upwards toobliquely downwards with respect to the electron beam generator. As aresult, each particle is irradiated in a free-fall process from a pointobliquely above the electron source to obliquely below said source andis acted upon approximately from four sides in view of thetwo-dimensional fanning of the electron beams. Since a particle, e.g.grain, has a movement of its own when falling through the irradiationregion, the surface of the particles is acted upon with electron beamson all sides in this way and the surface dose is distributed in asubstantially homogeneous way.

The evacuation process of the electron beam generator (electron gun) andof the irradiation chamber is carried out such that air flows are alwaysdirected from the electron gun to the irradiation chamber or always fromthe electron beam generator and the irradiation chamber to the side ofatmospheric pressure when the irradiation chamber and the electron beamgenerator connected thereto are pumped and aerated.

The fast passage of the particulate material or bulk material from thepressure stage feeder which is arranged at the inlet side of theirradiation chamber and in which a pressure prevails above that of thewater bound in the surface of the material to be treated, e.g. grains,into the irradiation chamber at a substantially lower working pressure,as well as the short dwell time in the irradiation chamber effect asudden temperature decrease on the surface of the particulate materialor bulk material and thus a reduction of the evaporation rate of water.

The above object is attained according to the invention with respect tothe device for treating bulk material in particulate form, in particularseeds, with electron beams in a vertically arranged irradiation chamberwhich includes a top inlet opening and a bottom outlet opening for thebulk material and on which a plurality of electron beam generators areradially arranged, by the measures that the irradiation chamber isevacuated and its upper end is provided with a distributing device forseparating the particulate material, and the electron beam generatorsare equipped with deflection means for spreading the electron beams toform an irradiation field through which the particulate material exitingfrom the distributing device is moved in a free-fall process.

Hence, the evacuated irradation chamber is provided for receiving amaterial flow of particulate material in a free-fall process, with theparticle distance being increased in at least one irradiation field ofthe irradiation chamber, and that electron beam generators are arrangedradially relative to the material flow in the area of the irradiationfield and equipped with deflection means for spreading the irradiationfield swept over by the electron beams from several directions.

It is preferred that at least two electron guns are arranged on theirradiation chamber, preferably diametrally opposite to each other.

An adequate irradiation of the particulate material on all sides effectsan adequate separation of the material flow or bulk material flow ofparticulate material during passage through the irradiation field insidethe irradiation chamber. To this end, a distribution device ispreferably arranged at the entry point of the particulate material orbulk material into the irradiation chamber for separating the materialacross substantially the whole cross-section, namely at least inparallel with a main plane of the irradiation chamber and preferablytogether with a fall shaft arranged thereafter. An improved separationof the particles of the material or bulk material flow is also achievedby providing the irradiation chamber with a sufficient length invertical arrangement, so that the particles of the material or bulkmaterial flow are sufficiently separated in the irradiation region.

Furthermore, it is preferred that a pressure-stage feeder system for theintroduction and discharge of the particulate material or bulk materialinto and from the irradiation chamber (recipient) has pressure stageswhich are composed of a plurality of rotary vane feeders, at least therotary vane feeder closest to the inlet and outlet sides of theirradiation chamber being each speed-controlled and also active as adosage device.

Preferably, in the device according to a preferred embodiment of theinvention, the transport of the particulate material or bulk material iscontrolled before and after the respectively last pressure stage for theintroduction and discharge of said material in such a way that a columnof particulate material or bulk material is maintained whose axialextension, i.e. the height, is great in comparison with its diameter.This column acts as a flow resistance.

To avoid or suppress disadvantageous effects on the electron guns bysubstances which accompany the particulate material or bulk material andare introduced together with the material into the irradiation chamber,the guns are provided in the beam generator with a plurality ofsuccessive shutters whose diameter is adapted to the associated electronbeam, preferably increases towards the beam exit side when fannedelectron beams are used. Vacuum generators are radially connectedbetween adjacent shutters. It is also preferred that an aerationconnection which can be throttled is provided between the two shuttersclosest to the beam exit of the electron beam from the associatedelectron gun.

In a preferred embodiment of the device according to the presentinvention, a distribution device which evenly distributes the materialor bulk material with the aid of guide plates substantially over thewhole cross-section (at least in the direction of a main plane) of afall shaft arranged directly after the distribution device is providedat the entry point of the particulate material or bulk material, such asgrains, into the irradiation chamber. At least two electron beamgenerators (electron guns), preferably axial guns, are preferablyarranged at the same level radially opposite to each other in theirradiation region arranged after the fall shaft. The associateddeflection means of the electron guns fan the respectively associatedelectron beam over a great width. Each electron beam is periodicallydeflected in the conventional way by means of deflection generatorshorizontally and vertically. The electron guns have a plurality ofshutters whose diameter is adapted for guiding the electron beam in theelectron gun, preferably increases continuously towards the beam exitside.

A connection to the atmosphere which is adjustable by means of athrottle valve and preferably serves to aearate the irradiation chamberand the associated electron beam generator is preferably providedbetween the beam exit side and the shutter adjacent thereto. However, apermanent dosed supply of a flow medium from the electron beam generatorto the irradiation chamber may optionally take place in this way foradditionally preventing dust from entering from the material in theirradiation chamber into the electron gun. Radial vacuum generators-arepreferably connected between the other shutters. The irradiation chamberpreferably has a sufficient length in vertical direction to effect orsupport the separation of the particles during the free fall of theparticulate material or bulk material in said chamber.

The guide plates of the distribution device are preferably arranged inthe manner of fans for separating the particulate material or bulkmaterial inside the irradiation chamber (recipient) for dividing thematerial., or bulk material flow.

Other preferred embodiments of the invention are outlined in theremaining subclaims.

The process and the device of the invention are especially intended forthe treatment of seeds as bulk material or particulate material torender ineffective harmful organisms adhering to the seeds. Generally,the process and the device according to the present invention areespecially intended to improve the properties of particulate material orbulk material which is moist and/or dusty. As for an efficient treatmentof the material with electron beams in vacuum, these accompanyingfeatures create special problems with respect to an efficient procedureand a long-term operation of the electron generators that must above allbe protected against dust.

Apart from the combat against harmful organisms on seeds, the processand device according to the present invention could also be used fortreating granules, catalysts or ceramic bodies for the chemical industryor for other applications.

Materials having relatively disadvantageous properties or adisadvantageous composition for electron beam treatment in vacuum, e.g.,a high water and dust content, can also be treated in the process anddevice of the invention for treating particulate material or bulkmaterial although e.g. dust adhering to the material is above all to beprevented from being released into the irradiation chamber and is to bekept away from the electron beam generators as much as possible.Especially decoupling under vacuum which is carried out during thesupply of the material to the irradiation chamber serves to achieve thisobjective as far as the present invention is concerned.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall now be described with reference to an embodiment andaccompanying drawings, in which:

FIG. 1 is a diagrammatic longitudinal and sectional view of a device fortreating grains in accordance with the present invention;

FIG. 2 is a partial view of an upper inlet portion of the device of FIG.1 in a plane offset by 90° relative to the representation of FIG. 1.;

FIG. 3 is a diagrammatic partial view of the device according to FIG. 1in the area of the irradiation chamber with associated electron beamgenerators;

FIG. 4 is a current density profile of an electron beam in the area ofan irradiation field of the irradiation chamber.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the invention for the treatment of particulate material(bulk material) shall be explained in the following. The particulatematter in this embodiment is seeds, in particular grains. The inventionis of course not limited thereto. Rather, any other organic and/orinorganic material in particulate form that is to be subjected toirradiation with electron beams can be treated as treatment material inthe process and in the device of the invention.

FIG. 1 is a diagrammatic longitudinal and sectional view illustratingthe procedure as well as the device for treating grains with electronbeams.

An irradiation chamber 1 (recipient) is provided with pressure stages 3,4 for the introduction and discharge and for the formation of acontinuous flow of grains 2. Each of these pressure stages consists oftwo rotary vane feeders 5, 6 and a connection 7 for pressure pumps, inparticular vacuum pumps, to build up pressure gradually during thetravel of grains 2 towards the evacuated irradiation chamber 1 and toensure the necessary pressure conditions for possibly another subsequenttreatment or discharge of grains 2 after irradiation chamber 1 has beenleft. A plurality of pressure stages 3, 4 may optionally be arranged oneafter the other at both the inlet side and the outlet side, especiallyin response to the pressure difference to be controlled. Grains 2 may besupplied at the inlet side into the device from a silo 20 or anothergrain supply container.

As is especially illustrated in FIG. 2, which shows a transition regionbetween irradiation chamber 1 and the pressure stage at the inlet sidefor the supply of the material flow of grains 2, a distribution device 8is provided in a transition region towards irradiation chamber 1 afterthe preceding pressure stage 3 with rotary vane feeders 5, 6 forseparating grains 2. This distribution device 8 includes guide plates 9arranged in fan-shaped fashion for distributing the flow of grains 2over a greater cross-sectional area.

The separated grains 2 pass from fall shaft 10, which is arrangeddownstream of distribution device 8 and already forms part of theevacuated irradiation chamber 1, in a free-fall process into anirradiation field 1! of the evacuated irradiation chamber and fill thecross-section thereof essentially completely at least in the directionof a main plane determined by distribution device 8. The irradiationfield is determined by two opposite electron guns 12 flanged via scanner13. Each grain 2 is irradiated at two sides approximately at the sametime owing to the two, diametrally opposite electron guns 12. As aresult, grains 2 which rotate during their free fall are irradiated onall sides. On account of the arangement and configuration of the guideplates 9 of distribution device 8, grains 2 have about the same speedand, when passing through irradiation field 11, they are spaced fromeach other at a distance corresponding at least to the grain size.

Electron guns 12 respectively produce an electron beam 15. Electronbeams 15 are spread vertically and horizontally in the plane ofprojection of FIG. 2 in such a way that they cover the wholecross-section of the material flow of grains 2. The transparency of thebulk material flow of grains 2 which exists in the direction ofirradiation due to electron beams 15 is preferably about 50% inirradiation field 11 to avoid a mutual shadowing of grains 2 to asubstantial degree. Of course, it is also possible to operate at ahigher transparency of the material flow of grains 2. In this casehigher power loss portions must be accepted.

The deflection functions for the electron beam generators are chosensuch that the radiant power is evenly distributed over the width of thebulk material flow and that a current density profile is created inirradiation field 11 in the direction of the falling grains 2, as isshown in FIG. 4. This irradiation field 11 is preferably divided intothree regions which follow each other in the direction of fall of thegrains and of which two irradiation regions 11.1 and 11.2 have a highcurrent density, said irradiation regions 11.1, 11.2 being separatedfrom each other by an irradiation region 11.3 of a small or disappearingcurrent density. The dose homogeneity is improved over the surface ofgrains 2 due to the angular scatter of the electrons without anysubstantial energy loss. To prevent grains 2 from shadowing one another,the distribution of the bulk material flow of grains 2 in irradiationchamber 1 is chosen such that grains 2 move away from one another atsuch a mean distance that on account of the angle of deflection of anelectron beam 15 they are reached at least in one of irradiation fields11.1 or 11.2 by electron beam 15. A mean distance which corresponds tothe grain dimension is required for a vertical deflection angle of 45°.Since the current density is substantially reduced in the center regionof irradiation field 11, sensitive components of the oppositely arrangedelectron guns 12 are not considerably stressed by electron beams 15. Theconfiguration of irradiation field 11 with irradiation fields 11.1 and11. of a high current density is determined by the deflection functionin the vertical and horizontal directions. The line frequency is fixedsuch that the fall time of the grains through irradiation fields 11.1and 11.2 is composed of a plurality, e.g. 10, deflection periods. Thedensity of the line raster which is determined by the ratio of linefrequency to picture frequency determines the homogeneity of the currentdensity distribution in the direction of the falling grains. In apreferred embodiment, the line frequency of electron beam 15 isrespectively chosen such that it is at several kHz, and the picturefrequency is preferably within the range of some 10 Hz to some 100 Hz.Electron beam power losses due to a long optical path up to the mainplane of the bulk material flow of grains 2 can be compensated throughthe selection of these parameters of the deflection function, as well asblanking and other influences.

Another advantageous feature regarding the improvement of thehomogeneity of the surface dose on the irradiated grains 2 is obtainedin that an evacuation pressure of about 10 Pa to some 100 Pa, inparticular about 100 Pa to some 100 Pa, is adjusted in irradiationchamber 1, whereby an angular scatter of the accelerated electrons isachieved without any objectionable energy losses.

As becomes apparent from the partial view of FIG. 3, electron guns 12respectively have a plurality of shutters 14 arranged in sequentialorder. The diameter of these shutters constantly increases in thepresent case in the direction from the beam generator to the exit ofelectron beam 15. A connection 16 to the atmosphere is provided viavalve 17 between the last shutter 14.2 at the exit side and thepreceding shutter 14.1. Vacuum generators 18 are respectively connectedbetween the other shutters 14. The penetration of foreign matter, inparticular of water vapour and-dust, from the grains in treatmentchamber 1 into electron guns 12 can effectively be prevented in thisway. Valve 17 serves to aerate the device, with air flows being alwaysdirected during pumping and airing away from electron gun 12 towardsirradiation chamber 1 or in conjunction with the evacuation processalways away from electron gun 12 and irradiation chamber 1 to the sideof the atmospheric pressure. Such a connection 16, however, mayoptionally be used for generating a constant dosed flow of a flow mediumfrom electron gun 12 to irradiation chamber 1 to additionally preventthe penetration of dust into electron gun 12.

After having moved through irradiation region 11 in a free-fall processwithin the evacuated irradiation chamber 1, grains 2 are discharged atthe outlet side from a bottom outlet opening of irradiation chamber 1through pressure stage 4 with rotary vane feeders 6, 5 under pressurecontrol at connection 7 by means of a vacuum pump or other pressurecontrol devices in response to the pressure desired after the electronbeam treatment during the further transport of grains 2.

In response to the treatment conditions, in particular the configurationand control of the cross-sectional distribution of a material flowwithin irradiation chamber 1 through distribution device 8, it is ofcourse possible to provide another number of electron beam generators inanother radial and/or axial arrangement relative to irradiationchamber 1. The only thing of importance is that an irradiation of theindividual particles of the material or bulk flow is achieved on allsides together with a surface dose distribution which is as homogeneouspossible, namely through the joint action of both the processing of thematerial or bulk material flow for separating the particles during theirfall through the irradiation chamber and the arrangement as well asradial or axial distribution of the electron beam generators theirradiation chamber in consideration of the particles own motion in thematerial or bulk material flow. With a substantially "disc-shaped"cross-section of the flow of grains 2, as shown in the presentembodiment in FIGS. 1 and 2, the arrangement of opposite electron beamgenerators 12 is sufficient for obtaining a good irradiation result. Inresponse to the configuration of the assembly of the electron beamgenerator for forming an irradiation field, it is of course alsopossible to form another current density profile than the one shown inFIG. 4. The adaptation of these parameters depends on the type of thematerial to be treated, the spatial distribution of the material in theirradiation field, the desired irradiation result and other factors.

Grains 2 can be exposed to electron beams 15 for a sufficiently longtime and on all sides due to the opposite arrangement of electron guns12 according to FIG. 1 and the deflection as well as the wide spreadingof electron beams 15 relative to electron guns 12 obliquely upwards andobliquely downwards.

As illustrated, grains 2 are supplied from silo 20 via one or severalpressure stages 3 to distribution device 8 and irradiation chamber 1.The pressure at pressure stage 3 or between the individual pressurestages 3 is adjusted by the individual vacuum generators, connected toconnections 7 at each pressure stage, in such a way that the vapourpressure of water within the near-surface layer of grains 2 is notfallen below. The evacuation efforts on the whole are minimized for thevacuum generators owing to this pressure adjustment. Rotary vane feeders6 rapidly transport the bulk material or grains 2 into irradiationchamber 1 in which they move in a free-fall process under a pressurewhich is determined by the requirements of electron beam 15, acting onthe separated grains 2, and which preferably lies between about 100 Paand some 100 Pa. The stay time of grains 2 in irradiation chamber 1 isvery short owing to this conveying principle. As a result, the waterdischarge from grains 2 as well as evacuation efforts can be kept small.A further reduction of the water vapour discharge is achieved throughthe sudden temperature reduction which is effected by the rapidtransition of the pressure at the last stage of the pressure-stagefeeder system at the supply side (pressure stage 3) to the workingpressure in irradiation chamber 1. This temperature reduction is limitedto the near surface layer of grain 2 because of the relatively greattime constant for the temperature compensation in grain 2. Theevaporation rate is also reduced on the grain surface owing to thistemperature reduction.

The rotary vane feeder 5 at the inlet side is preferablyspeed-controlled and simultaneously serves as a dosage device. In a line19 it forms a column of bulk material, here grains 2, upstream ofpressures stage 3. This column acts as an additional flow resistance ifthe length of this column of accumulated grains 2 is large in comparisonwith the cross-sectional dimensions of said column.

The discharge of grains 2 from irradiation chamber 1 is carried out inan analogous way as the introduction thereof, the respective pressure atthe indiviudal pressure stages 4 being also kept above the vapourpressure of the water. The delivery pressure is gradually raised againto atmospheric pressure through pressure stage 4 or a plurality of suchstages disposed in series arrangement downstream of irradiationchamber 1. In this case, too, the rotary vane feeders 5, 6simultaneously serve the dosage of the grain flow. Like in the case ofthe first rotary vane feeder 5, it is also advantageous to provide arespective line section in front of the last rotary vane feeder 5 at thedischarge side, the length of this line section being great incomparison with the cross section thereof so as to form an additionalflow resistance at this place, too. Rotary vane feeder 6 which isarranged after irradiation chamber 1 preferably forms a speed-controlleddosage device as well.

In the present embodiment the invention has been described with respectto the electron treatment of a flow of grains for treating the latteragainst seed-borne harmful organisms. This method and the associateddevice accomplish an irradiation of the seeds which has a widefungicidal spectrum of effect without causing any produce-affectingdamage. Since the seeds are guided to and away from irradiation chamber1 via pressure stages in a vacuum-decoupling way, it is possible to keepdust which adheres to the seeds away from the treatment chamber and fromthe electron beam generators to a substantial degree. Moreover, oneachieves a high throughput with reduced dwell times in the irradiationchamber and, despite the high water content of the seeds, considerablyincreased evacuation efforts are not necessary.

Therefore, the process and the device according to the present inventionare especially suited for a continuous treatment of seeds, in particulargrain, in a continuous process to combat harmful organisms, without theinvention being limited thereto. Rather, other particulate material,granules, small ceramic balls, etc. can be treated for irradiation withelectron beams on all sides, and also other types of bulk material, inthe inventive process and in the device according to the presentinvention. The conduction of the evacuation process, the arrangement anddistribution, especially, of more than two electron beam generators onthe recipient, and the formation of the irradiation field and theselection of the cross-section of the material flow in the irradiationchamber in conjunction with the supply and discharge of the materialflow via a pressure-stage feeder system can be modified accordingly independence upon the respective treatment task. The invention achieves aconsiderable improvement of the throughput capacity together with ahomogeneous dose distribution over the whole surface of the particulatematerial or bulk material.

We claim:
 1. A device for treating bulk material in particulate form,which comprises electron beams in a vertically arranged irradiationchamber which includes a top inlet opening and a bottom outlet openingfor the bulk material having a pressure-stage feeder system connected toa vacuum source for introducing and discharging said bulk material, saidpressure stages being composed of a plurality of rotary vane feeders anda distribution device being arranged at an inlet point of said bulkmaterial into said irradiation chamber for separating said materialsubstantially across the whole cross-section of said irradiationchamber, and on which a plurality of electron beam generators areradially arranged, and wherein said irradiation chamber is evacuated,and said electron beam generators are equipped with deflection means forspreading said electron beams to form an irradiation field through whichsaid particulate material exiting from said distributing device is movedin a free-fall process.
 2. The device according to claim 1, wherein,saidirradiation chamber comprising a fall shaft for said bulk material aftersaid distribution device, at least two electron guns with deflectionmeans for fanning said electron beam being arranged in the area of thefree fall of said bulk material within said irradiation chamber radiallyrelative to the flow of bulk material, said electron guns eachcomprising a plurality of shutters with an opening diameter for saidelectron beam, a connection for aerating said irradiation chamber via avalve being provided between a shutter closest to the beam exit side andan adjacent shutter, and vacuum generators being respectively arrangedbetween said other shutters of said electron guns.
 3. The deviceaccording to claim 2, wherein said plurality of shutters have diameterswhich increase towards the beam exit side of said electron guns and arerespectively arranged inside said electron guns.
 4. The device accordingto claim 1, wherein said distribution device has guide plates arrangedin the manner of fans.
 5. The device according to claim 1, wherein twoelectron guns are arranged on said irradiation chamber in adiametrically opposite manner at the same level and said irradiationchamber has such an axial length that said bulk material is separatedduring its free fall in said irradiation field.
 6. The device accordingto claim 1, wherein at least said rotary vane feeder which is acted uponat the inlet side by atmospheric pressure is speed-controlled.
 7. Thedevice according to claim 6, wherein said rotary vane feeder forintroducing said particulate material or bulk material has a dosagedevice arranged upstream thereof.
 8. The process for treating bulkmaterial in particulate form which comprises the steps of:separatingsaid bulk material into dosed amounts at an inlet side of an evacuatedirradiation chamber; supplying said dosed amounts of the bulk materialto said irradiation chamber via at least one pressure stage comprising aplurality of rotary vane feeders connected to a vacuum pump; separatingsaid dosed amounts of said bulk material into separate particles througha distribution device being arranged at an inlet point of said bulkmaterial into said irradiation chamber and moving said particles in acontinuous free fall process through said evacuated irradiation chamber;treating said particles with a plurality of electron beams within anirradiation field in said irradiation chamber by irradiating saidparticles within said irradiation field on substantially all sides bysaid electron beams which are spread in the direction of fall of saidparticles and positioned from several sides and in several differentdirections; and discharging said irradiated particles from saidirradiation chamber via at lest one further pressure stage, comprising aplurality of rotary vane feeders connected to a vacuum pump, therebydischarging the treated particulate material in dosed amounts.
 9. Aprocess according to claim 8, wherein said particulate material in saidirradiation field is acted upon by said electron beams at least partlyalong a path which begins above the exit point of said electron beamfrom an electron beam generator and ends below said point.
 10. A processaccording to claim 9, wherein the particles of said material flow passthrough said irradiation chamber, in particular said irradiation field,separately at a transparency in the irradiation region of saidirradiation field of about 50% and at a mean distance between saidparticles in a direction transverse to the direction of said materialflow which is greater than the particles size.
 11. The process accordingto claim 8, further comprising the step of: adjusting the currentdensity profile of said electron beams in said irradiation field in sucha way that the dose of irradiation of the particles passing through saidirradiation field and forming said material flow is substantiallydistributed in a homogeneous way over the surface of said particles. 12.The process according to claim 11, wherein said irradiation field ofsaid electron beams is chosen such that two regions of a high currentdensity that are successive in the flow direction of said material flowand acted upon in a sufficiently uniform way across the cross section ofsaid material flow are separated from each other by a region of reducedcurrent density.
 13. The process according to claim 8 further comprisingthe step of:supplying a moist or dusty bulk material in particulate formto said pressure stage closest to said irradiation chamber at the inletside, at a pressure which corresponds to at least the vapor pressure ofwater on the surface or in the near-surface layers of said particulatematerial, such that the release of water, gases or dust from saidparticulate is as small as possible.
 14. The process according to claim13, wherein evacuation products from said particulate material areprevented from flowing into said electron beam generators by controllingthe evacuation process in said irradiation chamber and said electronbeam generators, preferably gas flows in said irradiation chamber arealways bound to flow away from said electron beam generators.
 15. Theprocess according to claim 14, wherein air flows are always directedfrom said electron beam generator and said irradiation chamber to theatmospheric pressure side during evacuation and aeration due to thecontrol of the evacuation process.
 16. The process according to claim 8,wherein a pressure of about 10 Pa to some 100 Pa is adjusted in saidirradiation chamber.
 17. The process according to claim 8, wherein aline frequency of said electron beams is adjusted to several kHz and apicture frequency to about some 10 Hz to some 100 Hz.